1. Field of the Invention
This invention relates to in-tube fluid-channeling baffles for air-cooled vacuum steam condensers and, more particularly, to new fluid-channeling baffles for installation inside steam condensing tubes to prevent fluid flow disruptions between the high velocity upwardly flowing steam and the downwardly flowing condensate which degrades the tube heat-transfer rates in bundles that employ cost-saving, long-length, heat exchange tubes.
2. Summary of the Background Art
This invention relates to cost-related improvements in the apparatus of the type disclosed in U.S. Pat. No. 4,905,474 entitled Air-Cooled Vacuum Steam Condenser. The present invention permits the use of cost-saving, longer length, steam condensing tubes and also increases the overall heat transfer efficiency. It concerns the design of new fluid-channeling baffles installed inside some of the finned steam-condensing tubes.
U.S. Pat. No. 4,905,474 describes an A-frame type of bundle and fan arrangement where the steam and condensate movement inside the finned tubes is counterflow. The steam moves upward into and through the tubes while the condensate flows downward by gravity back to the steam source.
When certain tube lengths are exceeded, a condensate flow problem occurs inside the steam condensing tubes. Depending on factors such as the steam velocity entering the tubes, steam density, tube diameter and tube shape, fluid flow turbulence or disruptions can occur. Condensate flowing down the bottom of the tube in an orderly stream manner is interrupted by high velocity steam flowing upwardly in the opposite direction. The kinetic energy of the steam velocity is transferred to the condensate with many different forces playing a key role. Such forces include gravity, momentum, friction and surface tension. The net result is that both vapor-shear and gravity forces take control of the condensate fluid flow which becomes erratic, wavy and stratified. Slugs of liquid are momentarily formed that block the normal flow of steam and condensate inside the tubes. Depending upon the severity of the situation, the condensate may periodically hold-up inside the tubes and flow out of the ends in spurts and globs accompanied by some turbulent fluid noises.
This unsteady fluid flow along sections of the tube length creates thick condensate films on the wall surfaces that act as heat insulation. This degrades the log-mean-temperature-difference (LMTD) and the overall heat transfer rates of the process. It also hastens condensate freezing in some localized areas of the tubes.
This erratic pulsating condensate flow problem can be avoided by preventing it from occurring before it starts. The fluid boundary between condensate and steam flowing inside and inclined tube is horizontal, therefore, if a horizontal baffle were installed to continue the fluid separation by channeling it into the lower reaches of the tube where the most severe turbulent action takes place, this would essentially stop the interchange of energy. A baffle would prevent the high-velocity steam from imparting its disruptive energy to the condensate flowing in the opposite direction. There will be some steam flowing below the baffle and above the condensate stream, but it will be of no consequence since its energy content will be small and will be quickly dissipated compared to the energy content of the mass bulk of steam-flow above the baffle.
The region of disruptive flow is of some infinite tube length that starts at the tube entrance and stops at some point further up into the tube. In all cases the maximum steam velocity is at the tube entrance while the minimum, zero velocity, is at the rear header. The disruptive steam velocity starts at the tube entrance and ends at some mid-point well below the rear header depending on the many variable factors previously mentioned.
The baffle sections need not be installed in bundles with normal length steam condensing tubes. The baffle sections also need not be installed for the full tube lengths nor in all tube rows of bundles with long tubes. They should only be installed in those portions of the tube lengths that have steam velocities high enough to cause flow disruptions. In addition, to save material costs, the baffle sections need not be continuous in length but can be interrupted with voids in-between. Some small condensate waves that may be induced in the short open sections will be quickly dampened after the flow passes the next baffle section.
The condensate flowing on the bottom of the tubes is reheated by warm metal tabs protruding downward from the new baffle plates. The baffle plates are surrounded by steam so that its temperature is very nearly that of the saturated steam. These tabs are designed and positioned in the condensate stream path to maximize heat transfer to the condensate. The higher the condensate temperature that is returned to the power plant cycle, the higher the plant thermal efficiency.
As illustrated by a great number of prior patents and commercial devices, efforts are continuously being made in an attempt to improve air-cooled vacuum steam condensers. Such efforts are being made to render such vacuum steam condensers more efficient, reliable, inexpensive and convenient to use. None of these previous efforts, however, provide the benefits attendant with the present invention. Additionally, prior patents and commercial devices do not suggest the present inventive combination of component elements arranged and configured as disclosed herein. The present invention achieves its intended purposes, objects and advantages through a new, useful and unobvious combination of component elements, with the use of a minimum number of functioning parts, at a reasonable or lower cost to manufacture, and by employing only readily available materials.
Therefore, it is an object of the present invention to provide an improved device for condensing steam, the device including a bundle of long heat-exchange tubes extending from first and lower header means to second and upper header means defining paths for the steam as it moves from the lower header means toward the upper header means and for effecting a flow of steam upwardly and a flow of steam condensate downwardly within the tubes, and baffling located in some of the tubes of the bundle to channel and thus separate the bulk of the upward flow of steam from the bulk of the downward flow of the condensate.
It is a further object of the present invention to prevent high-velocity vapor fluid forces from opposing and disrupting the gravity flow of condensate inside a tube.
It is a further object of the present invention to channel and thus separate the bulk flow of the two fluids, a vapor and a liquid, thereby preventing the kinetic energy of one fluid from imparting its disturbing and disruptive energy to the other fluid.
It is a further object of the present invention to position a perforated baffle within a heat-exchange tube having liquids and vapors flowing in opposite directions so that its metal protrusions will reheat the flowing condensate.
It is a further object of the present invention to permit the use of longer and more economic steam condensing tubes without experiencing heat transfer degradation caused by disruptions in the fluid flow.
It is a further object of the invention to improve the overall heat transfer rates of condenser tubes which have baffles.
It is a further object of the present invention to increase the condensate temperature of those sections of tubes which have baffles.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiments in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.